Prophylactic bactericidal implant

ABSTRACT

A medical implant system is described for inhibiting infection associated with a joint prosthesis implant. An inventive system includes an implant body made of a biocompatible material which has a metal component disposed on an external surface of the implant body. A current is allowed to flow to the metal component, stimulating release of metal ions toxic to microbes, such as bacteria, protozoa, fungi, and viruses. One detailed system is completely surgically implantable in the patient such that no part of the system is external to the patient while the system is in use. In addition, externally controlled devices are provided which allow for modulation of implanted components.

REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/585,159, filed Jul. 1, 2004, the entire contentof which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to systems and methods for inhibition of microbialinfection related to surgical implant devices. In particular, theinvention relates to systems and methods for inhibition of microbialinfection related to orthopedic implants.

BACKGROUND OF THE INVENTION

Joint degeneration is the leading chronic condition in the elderly; itaffects one in every eight Americans and almost half the population overthe age of 65. (Brooks, P. M, Med. J. Aust., 173:307-308, 2000) The mostcommon form of joint degeneration is osteoarthritis. Osteoarthritisweakens and breaks down cartilage and bone, causing pain as bones rubtogether. Eventually the constant rubbing of the bony surfaces destroysthe surfaces that are rubbing against one another leading to rough,painful movement. Total joint replacement, or arthroplasty, represents asignificant advance in the treatment of painful and disabling jointpathologies. Arthroplasty can be performed on almost any joint of thebody including the hip, knee, ankle, foot, shoulder, elbow, wrist, andfingers. Total joint replacement: whether hip, knee, ankle, foot,shoulder, elbow, wrist, and fingers or other, is typically done as afinal stage treatment for a patient who suffers from some form of jointdegeneration.

In its early stages, many people manage arthritis pain conservatively byusing anti-inflammatory medicines, weight reduction, lifestylemodification, physiotherapy, or occupational therapy. However, as thedisease progresses the pain intensifies. When the pain gets to the pointwhere everyday, normal activities such as putting on shoes and socks orwalking up stairs become too painful, total joint replacement surgery isan attractive option to restore movement and independence, and todramatically reduce pain.

Although joint replacement is a relatively large field withinorthopedics, the number of fracture fixation devices utilized around theworld far outranks the number of artificial joints. Fracture fixation isgrowing daily as the number of fractures associated with traumaaccidents is increasing. Fixation devices can be internal or external innature and include devices such as a plate, wire, screw, pin, rod, nailor staple, which aid in maintaining fracture fragments in properposition during healing. Such devices are usually inserted after openreduction of the fracture and will remain for the entirety of thehealing process, often becoming a permanent structure within the body.

Joint replacement surgery began in the early 1950's, and its frequencyhas grown as surgical techniques and medical care associated withsurgery improves. In the late 1980's between 500,000 and 1 million totalhip replacements were performed per year, while in 2004 it is estimatedthat approximately 600,000 joint prosthesis and 2,000,000fracture-fixation devices will be inserted into patients in the UnitedStates.

Unfortunately, as the number of implant surgeries increases, the numberof associated infections also increases. Any person who has an implantis at risk for developing an infection associated with the device. It isestimated that 2% of joint prostheses and 5% of fixation devices willbecome infected. Taking 3% as an average estimate of infected implants,as many as 30 million incidents of infection may occur.

The effects of implant infection are expensive as well as a danger tothe health and well-being of the affected individual. For example,infection results in direct medical and surgical costs and additionallymay cause patient pain, suffering, lost wages, lost work and decreasedproductivity. On average an infected hip prosthesis patient spends sixtimes the number of days in the hospital when compared to thenon-infected prosthetic hip patient. In 1991, the total cost of aninfected patient, both in hospital and as an outpatient, was $45,000 ascompared to the total cost of $8,600 associated with a non-infectedpatient. (Bengston, S., Ann. Med., 25:523-529, 1993)

Joint replacement implants and fixation devices include a variety ofmaterials foreign to the human body, such as metals, plastics, andpolymeric substances, all of which have the potential to serve assubstrates for attachment and growth of microorganisms.

In particular, certain microorganisms may exude a glycocalyx layer thatprotects certain bacteria from phagocytic engulfment by white bloodcells in the body. The glycocalyx also enables some bacteria to adhereto environmental surfaces (metals, plastics, root hairs, teeth, etc.),colonize, and resist flushing.

Once microorganisms colonize an implant, it is often very difficult toeradicate or even inhibit the infection. For example, systemicadministration of antibiotics is often ineffective due to limited bloodsupply to the areas of the implant. Additionally, many bacterial speciestoday are resistant to antibiotics.

Where infection cannot be inhibited it may spread and become even moreserious, as in patients who have an infection within the bone,osteomyelitis. Such patients often must undergo a difficult and costlytreatment involving extended hospitalization, joint debridement,aggressive antimicrobial therapy, total joint removal followed by totaljoint replacement and possible amputation if the infection can not beeliminated.

Since implantation of an orthopedic implant device, such as a jointreplacement prosthesis or fixation device, is quite common andassociated infection frequent, there is a continuing need for newapproaches to inhibition of infection. In particular, it would be verydesirable for both the physician as well as the patient to be able totreat a prosthetic osteomyelitic infection without the removal of animplant. Further, economical and safe apparatus and methods ofinhibiting implant associated infections are needed.

SUMMARY OF THE INVENTION

A medical implant system is provided which includes an orthopedicimplant body made of a biocompatible material. In one option, theimplant body is a joint replacement prosthesis implant. In a furtheroption, the implant body is an orthopedic fixation device. Optionally,more than one implant body is provided as part of an inventive system.The implant body has an external surface and a metal component isdisposed on the external surface of the implant body. An inventivesystem further includes a conduit for electrical current wherein theconduit is in contact with the metal component. A power source is alsoincluded which is in electrical communication with the conduit forelectrical current. More than one power source may be provided, forexample, where more than one implant body is included.

Optionally, an implant body is a joint replacement prosthetic implant.In a further option an implant body is a part of a joint replacementprosthetic implant

In one embodiment, an internal cavity having a wall and an opening isincluded in the implant body and a cap is provided to close the openingof the internal cavity. A power source is positioned in the internalcavity. The conduit for electrical current provided in such anembodiment is optionally the implant body itself. Thus, a current fromthe power source may be connected to the metal component through thebiocompatible material of the implant body.

In a further option, the implant body is adapted to be disposed totallywithin a human body when in use as an implant.

Also optionally, a metal component disposed on a portion of the internalcavity wall, preferably such that the portion of the metal component inthe cavity is continuous with the portion of the metal componentdisposed on the external surface of the implant body. Also preferably,the metal component in the cavity has the same composition as the metalcomponent on the external surface. Optionally, the form of the metalcomponent in the cavity is the same or different compared to the form ofthe metal component on the external surface. For example, a wire ormetal ribbon may be attached to the metal component on the externalsurface and to the cavity wall. In one embodiment, the metal componentin the cavity is in contact with a terminal of a power source disposedtherein.

In a preferred option, the metal component includes a transition metal,selected from gold, zinc, copper, cadmium, cobalt, nickel, platinum,palladium, manganese, and chromium. In a further preferred option, themetal component includes silver.

In a further preferred option, the metal component is more electricallyconductive than the biocompatible material of the implant body.

One form of a metal component is a coating disposed on the externalsurface of the implant body. Such a metal coating ranges in thicknessbetween 1×10⁻⁹-5×10⁻³ meters, inclusive.

Optionally, a metal coating disposed on a portion of the externalsurface of the implant body covers a portion of the external surfaceranging from 1-100% of the total external surface of the implant body.Further optionally, the metal coating disposed on a portion of theexternal surface of the implant body covers a portion of the externalsurface ranging from 50-99% of the external surface of the implant body.Preferred is a configuration in which the metal coating is disposed as asingle region of continuous coating on the external surface.

In one embodiment of an inventive medical implant system the implantbody includes an articular surface which does not include a metalcomponent such as a metal coating.

In another option, metal component is provided in the form of a wire,ribbon, or foil disposed on the external surface.

An inventive system may be configured such that the power source iscontinuously powering a current conducted to the metal component forrelease of metal ions. Alternatively, a system includes a switch forpowering the current on or off. In a further embodiment, the current ismodulated by circuitry adapted to control the current so as to increaseor decrease the amount of current flowing and the amount of metal ionsreleased. Thus, a resistor in electrical communication with the powersource is optionally included. In a preferred embodiment, the resistorand power source are positioned in an internal cavity of the implantbody. Optionally, a switch in electrical communication with the powersource is included to control the power source. Further optionally, acontroller in signal communication with the switch is provided. Such acontroller is operated to send a signal to a system component adapted toreceive the signal and to control the switch. Preferably, a controlleris external to an individual having the implant, such that activation ofthe switch may be performed by a doctor, technician or by the patient.

Also described is a method for inhibiting microbial infection associatedwith an orthopedic implant, which includes providing an inventive systemand delivering a current to a metal component disposed on an externalsurface of an implant body, the implant body located in a human body ata site of potential infection. Delivery of current to the metalcomponent is associated with antimicrobial action such as release ofmetal ions toxic to an infectious microbe at the site of potentialinfection, such that microbial infection is inhibited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a line drawing of an apparatus according to an embodiment ofthe invention in the form of a hip joint implant showing a portion ofthe exterior of the implant and a cut away portion;

FIG. 1A is a line drawing of an apparatus according to an embodiment ofthe invention in the form of a hip joint implant showing an exteriorview of the implant;

FIG. 2 is a line drawing of an apparatus according to an embodiment ofthe invention in the form of a hip joint implant having a power sourceexternal to the body of the patient;

FIG. 3 is a line drawing of a hip joint implant apparatus according toan embodiment of the invention, showing transmission of a signal to theapparatus in situ; and

FIG. 4 is a line drawing of an inventive bone screw implant body.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides methods and apparatus for prevention andinhibition of implant-associated infection.

A medical implant system is provided which allows for release ofmicrobe-inhibiting metal ions in the vicinity of a temporary orpermanent surgically implanted device. In particular, metal ions arereleased from a metal component of an implant by application of anelectrical current to the metal component. A power source for producingthe electrical current is provided which may be external to the implant,or preferably, contained within the implant.

A medical implant system is provided which includes an implant body madeof a biocompatible material. A metal component is disposed on theexternal surface of the implant body and a power source is included topower delivery of an electrical current to the metal component. Theelectrical current is delivered to the metal component via an electricalconduit. In a preferred embodiment, the metal component is differentthan the biocompatible material. Thus, where the biocompatible materialis a metal, the metal component differs in composition from thebiocompatible material. For instance, preferably, the metal componenthas a higher conductivity than the biocompatible material.

The term “implant body” as used herein refers to an orthopedic implantfor replacement or repair of a component of the musculoskeletal system.For example, an orthopedic implant includes a joint replacementprosthetic implant for joint replacement or repair. Prosthetic implantsinclude those for replacement or repair of any joint illustrativelyincluding a knee, a hip, an ankle, a shoulder, a wrist, and a finger ortoe joint among others. Further, an orthopedic implant is an orthopedicfixation device used in replacement or repair of a component of themusculoskeletal system, such as a plate, wire, screw, pin, rod, nail orstaple. In a preferred embodiment, an implant body is preferably animplant body which is wholly contained within a patient's body when inuse for the purpose of the implant.

The term “biocompatible material” as used herein refers to a materialwhich is relatively inert in use following surgical placement into anindividual such that adverse reactions such as inflammation andrejection are rare. The biocompatible material is sufficiently strongand durable to allow the implant to perform its intended function, suchas joint replacement or fixation. Exemplary biocompatible materialsinclude metal materials such as surgical stainless steel, titanium, andtitanium alloys; ceramics; plastics; and combinations of these.

The metal component includes a metal which inhibits infection bymicrobes, such as bacteria, protozoa, viruses, and fungi. Suchantimicrobial metals are typically transition metals illustrativelyincluding silver, gold, zinc, copper, cadmium, cobalt, nickel, platinum,palladium, manganese, and chromium. A metal component preferablycontains at least 50% by weight of an antimicrobial metal, furtherpreferably contains at least 75% by weight of an antimicrobial metal andstill further preferably contains at least 95% by weight of anantimicrobial metal. In another preferred embodiment, the metalcomponent is substantially all antimicrobial metal. The antimicrobialproperties of silver are particularly well characterized and a metalcomponent preferably contains at least 50% by weight silver, furtherpreferably contains at least 75% by weight silver and still furtherpreferably contains at least 95% by weight silver. In another preferredembodiment, the metal component is substantially all silver. Inparticular, the metal component is capable of releasing a metal ion whenan electrical current is applied to the metal component.

In a preferred embodiment, the metal component is in the form of acoating disposed on the external surface of the implant body. Thecoating can be applied by any of various methods illustrativelyincluding dunk coating, thin film deposition, vapor deposition, andelectroplating. The metal component in the form of a coating ranges inthickness between 1×10⁻⁹-5×10⁻³ meters, inclusive, preferably1×10⁻⁷-4×10⁻³ meters, inclusive, and more preferably between0.5×10⁻⁶-5×10⁻⁴ meters in thickness.

In an example including a silver coating metal component, the totalamount of silver used during the coating process ranges between 0.016grams in weight and 8.95 grams in weight. Such a coating is at least0.016 grams in weight in order for enough silver material to be presentfor the ionization to occur. The total weight of silver typically doesnot exceed 8.95 grams in order to maintain a nontoxic state for thepatient.

In an embodiment including a metal coating disposed on the externalsurface of the implant body, a metal coating is preferably disposed onat least 50% of the external surface of the implant body, and morepreferably a coating is disposed on at least 75% of the external surfaceof the implant body. In an embodiment including a metal coating disposedon the external surface of the implant body, the coating is optionallydisposed on substantially all of the external surface of the implantbody. In a further option, the implant body is coated with the metalcoating on substantially all of the external surface excluding one ormore articular wear surfaces. An “articular wear surface” is a portionof an implant body which is exposed to wear during normal use whenimplanted. For example, a hip joint implant includes articular wearsurfaces at the interface of the “ball” and “socket” components of thejoint prosthesis, that is, at the acetabular surfaces. Where the implantbody is a fixation device, it is preferred that the coating is presenton at least 50% of the external surface of the implant body, and more onat least 75% of the external surface of the implant body, and furtherpreferably on substantially all of the external surface of the implantbody, including threads where the device is a bone screw.

A metal coating is preferably disposed on the external surface as asingle continuous expanse of the coating material.

Optionally, the metal component is in the form of a wire, ribbon, orfoil disposed on the external surface of an implant body. Such a metalcomponent may be attached to the implant body by welding, by anadhesive, or the like.

In order to deliver an electrical current to the metal component andrelease antimicrobial metal ions, a power source is included in aninventive system. A power source may be any of various power sourcessuch as a battery, capacitor, or connection to external AC. Such powersources are known in the art.

In one embodiment of an inventive system, a power source is implanted inthe body of an individual receiving a joint prosthesis. An implant powersource in such an embodiment is self-contained, that is, requiring noconnection to external power. Illustrative examples include anelectrochemical cell such as a battery and a capacitor. In a preferredembodiment, the implant body has an internal cavity housing the powersource and, optionally, other components of the system, includingcircuitry adapted to modulate a current from the power source.

An internal cavity in an implant body includes a wall defining thecavity and an opening for insertion of a power source and, optionally,other components of the system.

In general, a preferred power source housed in an implant body cavity islightweight and sized to fit in the cavity. In addition, a power sourcehoused in an implant body cavity is capable of producing electricalcurrents in the range of 0.1-200 microamps. A power source housed in animplant cavity may be selected according to the requirements of apatient. For example, a temporary implant may not require a power sourcehaving as long a life expectancy as a permanent implant.

In a further embodiment, circuitry adapted to modulate an electricalcurrent is included in an inventive system. Metal ions can be mobilizedin greater quantities by increasing the current that is applied to theimplant. If the current is increased a greater concentration of metalions, preferably silver ions, will be provided near the surface of theimplant. The greater concentration of silver ions will create a greaterdiffusion constant and provide for a greater distance of penetration bythe ions. Similarly, current may be modulated to decrease ion release asdesired, such as where no infection is believed to be present.

For example, a resistor, a switch, a signal receiver, a relay, a signaltransmitter, transformer, a sensor, or a combination of these or othersuch components and connectors may be included, optionally configured asa circuit board arrangement. In a preferred embodiment, all or part ofthe circuitry adapted to modulate an electrical current included in aninventive system is housed in a cavity in the implant body of anorthopedic implant.

Thus, optionally, the internal cavity also contains a resistor formodulation of the current. For example, a resistor in series with abattery allows use of a larger size battery with a greater lifetime. Theresistor in series can be used to reduce current flow to a desiredlevel.

Once a power source capable of producing the required current and of theappropriate size is determined, a resistance can be calculated by usingthe equation; V=I*R .Where V is the voltage of the battery that has beenselected, I is the current, 1 microampere, and R is the resistance thatwill allow for the current to flow from the determined battery. Thisresistor then can be placed in series with the power source to yield therequired current. It is noted that neither the current nor the voltagedelivered from a power source will be altered by the size of theimplant.

In a specific example, a surface mounted chip resistor will satisfy therequirements of the resistor for use in this application. Surfacemounted chip resistors come in a variety of resistances, ranging form 1ohms up to 51 mega-ohms. Surface mounted chip resistors are manufacturedin a variety of sizes which will meet the size constraints. For example,the Ohmite, thick film high voltage SMD chip, series MMC08 will easilyfit within the shaft of the redesigned hip implant. The MMCO8 hasdimensions of over all length of 2.0 millimeters and over all width of1.25 millimeters. This particular resistor is manufactured in resistancebetween 100 ohms and 51 mega-ohms.

An inventive implant system may be configured such that a desired amountof an antimicrobial metal ion is released over a specified period oftime so as to optimize the inhibitory effects on undesirable microbesand minimize any unwanted side effects. In one embodiment, an inventiveimplant system is configured such that an included power source is incontinuous operation and metal ions are released continuously.

In a preferred option, a switch is included in an inventive system tocontrol current to flow from the power source to the metal component. Aswitch allows antimicrobial ions to be released during specified periodsof time by controlling current flow. For example, the switch is turnedon to activate current and release antimicrobial ions at regularintervals, such as once a week or once a month, for a time followingimplantation in order to prevent infection. Further, where an infectionis detected or suspected, the switch is activated to allow current flowand release of metal ions to combat the infection. An included switch iscapable of withstanding the current and the voltage transferred acrossit.

A switch is optionally and preferably controlled by a controllerexternal to the body of the individual having an implanted prosthesis.An external controller may emit a signal operative to control a switch.In one example, a magnetically controlled switch, such as a reed switchis used. Magnetically based switches that are externally controlled by acontroller are currently manufactured and are available from commercialsources. Such switches are controlled by a controller including a magnetwhich is placed in proximity to the switch in order to turn the switchon or off. For example, a magnet may be positioned in the vicinity of apatient's hip in order to activate a magnetically controlled switch inan internal cavity of a hip prosthesis implant. Thus, the switch is insignal communication of with the controller.

Optionally, a transmitter is included in an inventive system which is insignal communication with receiver circuitry adapted to operate a switchand modulate current flow. Preferably the transmitter is activatedexternal to the body of an individual having an implanted prosthesis asdescribed herein. For example, a radio frequency transmitter may be usedto transmit a radio frequency signal to receiver circuitry in theinternal cavity of the implant body adapted to operate a switch andmodulate current flow.

In a further embodiment, microchip circuitry, programmed to modulatecurrent flow is included in an inventive system. Preferably, themicrochip circuitry is included in a cavity of an inventive implantbody. In a further embodiment, such microchip circuitry may be implantedat a second location in the implant patient, such as just under theskin, to remotely control the current flow.

A sensor may be included to sense microbial growth, such as bacterialgrowth on an external surface of an implant body. Such a sensorcommunicates a signal indicating bacterial growth to circuitry adaptedto activate a switch, stimulating release of metal ions and inhibitingthe microbes.

Preferably, the implant body having a power source in an internal cavityis adapted to be disposed totally within a human body when in use. Thus,the implant body preferably has substantially the same dimensions andshape of a conventional implant body.

In a preferred option, a portion of the metal component is disposed inthe internal cavity. For example, in a preferred option, a metal coatingis present on a portion of the wall of the internal cavity. Such a metalcoating is preferably continuous with a metal component, such as acoating, disposed on the external surface of the implant body.Optionally, and preferably, a metal component present in the internalcavity is in electrical contact with one terminal of a power sourcepresent in the cavity. A metal component present in the cavity may alsobe in the form of a wire, ribbon, or foil. Preferably the metalcomponent in the cavity is in the same form as the metal componentpresent on the external surface of the implant body and is continuoustherewith.

In a preferred option, a metal component disposed on the externalsurface and/or internal cavity wall is more electrically conductive thanthe biocompatible material of which the implant body is made.

The internal cavity has an opening which can be closed using a cap whichmay be attached to the implant body, such as by a hinge, or completelydetachable.

In a preferred option, the cap is made of an electrically insulatingmaterial.

In a further option, an electrically insulating material is disposedbetween the external surface of the implant body and the metalcomponent.

A conduit for conduction of an electrical current from the power sourceis included in an inventive system. In one embodiment, the conduit isthe biocompatible material of the implant body. In a further embodiment,a power source is external to the body of the individual having theimplanted prosthesis and the conduit traverses the skin of theindividual, connecting the metal component disposed on the implant bodywith the external power source.

FIG. 1 illustrates an exemplary embodiment of an inventive apparatus 100in a partial external, partial cut away view. A drawing illustrating aprophylactic bactericidal hip implant is shown having a silver coating,depicted as stippling, on the external surface 120. An internal cavity170 is shown in cut away sectional view, shown as the stripe markedregion. This cavity allows for the internal placement of the battery,switch and resistor components. A switch 130, resistor 140 and battery150 are shown, which are contained in the cavity. The remaining end ofthe original shaft has been machined to form a cap 160 so that a pressfit of the cap 160 in cavity 170 can be obtained after assembly of theinternal components. In this example, no coating is present on surfacestending to wear due to interaction with other implant parts or naturalelements of the body, articular surfaces, shown without stippling orstripe marks at 180. This allows for a dead end electrical circuitbetween the battery and the external silver surface. Current will flowthrough the better conductor, the silver coating, to the externalsurface and thus avoid the much poorer conductor, internal residualhardware device.

FIG. 1A shows an external view of a hip implant body 100 illustrating ametal coating, such as a silver coating, shown as stippling, present onan external surface 120 of the implant body. The coating is present onthe cap 160 as well in this illustration but not on articular or wearsurfaces as shown at 180.

A conduit from one terminal of the power source and a metal component isoptionally provided in the form of a wire extending there-between. Asnoted above, a further connection between the metal component and asecond terminal of the power source is optionally provided.

In a further preferred embodiment of the invention, a metal component isin removable contact with the implant. For example, a metal component isin removable contact with an implant may have the form of a metal wirein contact with an implant surface.

In another embodiment of an inventive system, a conduit is providedwhich extends outside of the body of an individual having an implantprosthesis according to the invention. For example, a conduit isprovided in the form of a wire such that one end of the wire may bepositioned in proximity to the metal component of an implantedprosthesis, preferably in contact with the metal component in order todeliver current and release metal ions from the metal component. Theopposite end of the wire optionally may extend outside the body tocontact a power source. The conduit is optionally removed when risk ofinfection is low and may be repositioned for stimulation of metal ionrelease as desired.

FIG. 2 illustrates an inventive system 200 in the context of a humanbody including an external power supply 250 and a conduit 270 contactingan implant body 210 having a metal coating, shown as stippling, on aportion of the surface of the implant body 210. It will be noted that nocoating is present on an acetabular wear surface of the implantprosthesis. Further shown is the “cup” portion of a hip replacementimplant, marked by stripes.

Another embodiment of an inventive apparatus is shown in FIG. 3 whichshows an inventive system 300 including a hip replacement prosthesis 310in the context of a human body. Also shown is an external controllingdevice 390 which may be used to modulate current flow in an implantedprosthesis by acting on internal circuitry 380 in order to modulatedelivery of metal ions to inhibit microbes.

Joint replacement or repair implants include one or more implantableparts which may be included as an implant body in an inventive system.For example, a hip joint replacement implant typically includes afemoral part, replacing the natural femoral head, and a socket part, oracetabular cup or shell, replacing the natural acetabulum. While aninventive system is extensively discussed herein with regard to animplant body which is a femoral part of a hip joint replacementprosthetic implant, it is appreciated that the socket part, or cupportion of a hip implant prosthesis may also be included in an inventivesystem as an configured to include an internal cavity containing a powersource and other components as described herein. A further example ofjoint replacement implant parts include a wrist implant having a carpalcomponent, for instance present where a first row of carpal bones isremoved, and a radial part, for instance inserted or attached to theradius bone. The radial part may provide an articular surface forinteraction with a carpal part. Another example is a knee jointprosthetic implant, having a femoral part attached to the femur and atibial part attached to the tibia, each having an articular surface forinteraction with the other. It is appreciated that one or more parts ofan implant prosthesis may be configured to include an internal cavitycontaining a power source and other components as described herein.Thus, an inventive system may include more than one implant body. In afurther option, each of the multiple implant bodies may include a cavityand power source, and may further include other components, preferably aresistor and switch, as described. In a further option, multipleswitches may be controlled separately, for instance where one implantbody or region in the vicinity of the implant body is more vulnerable toinfection than another, a switch in that implant body may be activatedto turn on current in that implant body without turning on current inanother implant body.

As noted, an implant may be a temporary implant, intended to remainimplanted for a limited period of time, or a permanent implant, intendedto remain implanted long-term, even as long as the remainder of theindividual's life. One type of temporary implant is known as a “spacer”implant. A spacer implant typically has a similar size and shapecompared to a permanent or short-term implant. A spacer implant istypically implanted in order to maintain the spatial integrity of anarea where a permanent joint replacement implant will be positionedeventually. For example, where an individual has a badly infectedimplant which must be removed, a spacer implant may be implanted whilethe infection is being fought. An inventive system is particularlyadvantageous in such a situation since a synergistic effect of aninventive antimicrobial system with a course of systemic or localantibiotics is achieved. Further, an inventive spacer implant may lessenor eliminate the need for use of bone cement, currently used in thissituation. The insertion of a spacer implant would allow the patient tobe much more active than if the joint were filled with bone cement.Further, tissue encroachment at the site is decreased by placement of aspacer implant.

FIG. 4 illustrates an implant body in the form of a fixation device,particularly, a bone screw 10. An external surface 20 of the implantbody includes a metal component in the form of a continuous metalcoating, including coating on screw threads. Also shown is a switch 30,a resistor 40 and a battery 50 inserted in an internal cavity 70 shownin the cut away region marked by stripes. Also shown is a cap 60 forclosing the cavity and protecting the components disposed in the cavityfrom the external environment, as well as limiting exposure of cells tothe components disposed in the cavity. Also shown is a metal coating 80inside the cavity 70. Also shown is an embodiment in which a metalcoating is also present on the threads 90 of the illustrated bone screw.

In one embodiment a power source, such as a battery, having a firstterminal, a second terminal, and a potential difference between thefirst and second terminals, is provided. Further provided is a conduitfor an electrical connection between the first terminal and the metalcomponent. Also provided is a conduit for an electrical connectionbetween the metal component and the second terminal.

A method for inhibiting microbial infection associated with anorthopedic implant is provided which includes providing an inventivesystem as described and delivering a current to a metal componentdisposed on an external surface of an implant body, the implant bodylocated in a human body at a site of potential infection.

In one embodiment, an inventive method for inhibiting an infectiousorganism includes introducing an electrical current into a metalcomponent of an implanted joint prosthesis to release metal ions fromthe component. The metal ions have a biostatic or biocidal effect onmicroorganisms such that growth and/or attachment of microorganisms onthe implant and in the vicinity of the implant are inhibited.

As noted above, biocidal metals and ions include a transition metals andions. Preferred metals and ions include silver, gold, zinc, copper andcombinations thereof. Further, metals and ions such as cadmium, cobalt,nickel, platinum, palladium, manganese, chromium, and the like may beincluded.

Infectious organisms inhibited by such metals and metal ionsillustratively include bacteria, viruses and fungi.

Generally, such metal ions inhibit infection at concentrations rangingbetween 1×10⁻³ M-1×10⁻⁷ M, inclusive, and is preferably delivered inamounts sufficient to achieve a concentration in this range. Optionally,and preferably, metal ions are delivered in amounts sufficient toachieve a concentration in the range between 5×10⁻⁵ M-0.25×10⁻⁶ M,inclusive. In particular, silver ions are delivered in amountssufficient to achieve a concentration in the range between 5×10⁻⁵M-0.25×10⁻⁶ M, inclusive.

A metal ion is released from a metal component by application of anelectrical current to the metal component. Bone and soft tissue cellsare affected by electrical current and thus the amount of currentdelivered and the length of time for which it is delivered must beconsidered in the context of the proximity of the implant to such cells.The amount of a metal ion released is dependant on the strength andduration of the electrical stimulus which is adjusted accordingly.

Generally, a current in the range of 0.1 microamps to 200 milliamps isdelivered to a metal component. In general, a current is delivered to ametal component for periods of time ranging from about 1 minute tocontinuous delivery over the lifetime of the power source, that is,weeks, months or years. In general weaker currents are used forlonger-term treatments. Thus, in a preferred embodiment, 0.3-1.5micro-amperes of current is delivered in order to ionize a silversurface layer. Also preferred is an embodiment in which 0.8-1.2microamps of current is delivered to a silver coating.

Small electrical currents in the ranges described are sufficient toionize a solid silver coating, producing silver ions. Without wishing tobe bound by theoretical considerations, according to Faraday's law,under ideal conditions 4 micrograms of silver will be liberated per hourper micro ampere of current applied to silver. Calculation 1 belowdetails this.

$\begin{matrix}{\left( {1{µAMP}} \right)*\left( \frac{1\mspace{14mu} {Coulomb}}{1\mspace{14mu} {Amps}*{Sec}} \right)*\left( \frac{1\mspace{14mu} {Faraday}}{96,487\mspace{14mu} {Coulombs}} \right)*\left( \frac{107.868\mspace{20mu} {{gram}{AG}}}{1\mspace{14mu} {Fraday}} \right)*\frac{1*10^{6}\; {µg}}{1\mspace{14mu} g}*\left( \frac{3600\mspace{14mu} {Sec}}{Hour} \right)} & \left( {{Equation}\mspace{14mu} 1.0} \right)\end{matrix}$

Assuming the power source is capable of producing a 1 micro-amperecurrent and that the electrical current should not exceed 20micro-amperes at any time, 10 micrograms/milliliter concentration ofsilver ions within a couple of hours. Additionally the maintenance of a10 micrograms/milliliter concentration of silver ions is possible withvery small electrical current requirements.

Additional theoretical considerations indicate that total lifetimeexposure to silver ions advantageously do not exceed 8.95 grams for aperson of average size, approximately 70 kilograms, and having anaverage life expectancy, about 70 years. This calculation is based onthe assumption that about 0.35 milligrams of silver can be safelyconsumed each day, see Newman, J. R., Tuck Silver 100 Safety Report,Jan. 9, 1999. Thus, for a permanent implant, it is desirable that aninventive system not contain more than about this amount of silver.Similar calculations may be made for other metal ions as will berecognized by one of skill in the art.

In one embodiment, a method of inhibiting bacterial infection associatedwith an implant includes administration of a systemic or localantibiotic and administration of a metal antibiotic via an inventiveimplant. A synergistic effect of such treatment is achieved as a lowerdosage of both the systemic or local antibiotic and the metal antibioticis necessary to achieve a therapeutic effect.

While inventive methods and apparatus are generally described withreference to use in humans herein, the methods and apparatus are alsoused in other animals to inhibit infection. For example, an inventiveapparatus and method is used in animals illustratively including cats,dogs, cattle, horses, sheep, goats, rats, and mice.

The apparatus and methods described herein are presently representativeof preferred embodiments, exemplary, and not intended as limitations onthe scope of the invention. Changes therein and other uses will occur tothose skilled in the art. Such changes and other uses are encompassedwithin the spirit of the invention as defined by the scope of theclaims.

Example 1

An implant body is manufactured by obtaining a hip replacementprosthesis similar to a DePuy SUMMIT Tapered Hip System designed toinclude an internal cavity, about 10 millimeters in length and about 5millimeters in width and a cap to close the opening of the cavity asdescribed herein. Articular surfaces of the implant body are masked andthe remaining external surfaces are coated with a silver metal filmabout 1 micron in thickness. A battery, resistor and switch are chosento fit in the cavity. A portion of the cavity wall adjacent to theexternal surface of the implant body is also coated with silver metal toa depth adjacent the positive terminal of the battery.

A battery with the desired profile is currently in production by manybattery manufacturers. The Energizer battery number 337 satisfies all ofthe required size characteristics needed for implementation within abactericidal hip implant. When examining the Energizer 337 battery onecan see that the small size, 1.65 mm in height by 4.8 mm in diameterallow the battery to easily fit within the 5 mm compartment.

The 337 size battery provides a voltage of 1.55 volts, which is muchgreater than required for the application of ionizing a solid silvercoating. Thus, a resistor is chosen to be placed in series with thebattery. Using a voltage of 1.55 volts and a required current of 1micro-ampere one can calculate the required resistor as shown inEquations 2.1 and 2.2 below

$\begin{matrix}{V = {IR}} & \left( {{Equation}\mspace{14mu} 2.0} \right) \\{R = {\frac{V}{I} = {\frac{1.55\mspace{14mu} {volt}}{1*10^{- 6}\mspace{14mu} {amperes}} = {15,550\;,000\mspace{14mu} {ohms}}}}} & \left( {{Equation}\mspace{14mu} 2.1} \right)\end{matrix}$

The required resistor should have a resistance of approximately 15.5mega-ohms. Additionally the resistor must conform to the sizerequirements as set by the diameter of the pocket within the shaft ofthe implant, 5 millimeters.

Utilizing a resistor with the required 15.5 mega-ohms rating in serieswith the 337 battery will provide for approximately 75573 hours of runtime. The calculation of the run time for the battery under with thisresistance is show in calculation #3 below. During this running time thebattery will be producing the required 1 micro-ampere current that isrequired to ionize the solid silver coating.

$\begin{matrix}{\frac{{run\_ Time}({New\_ hip})}{{{MMCO}\; 8} - {Resistance}} = \frac{{run\_ Time}\left( {simulated\_ application} \right.}{{simulated}\text{-}{resistance}}} & \left( {{Equation}\mspace{14mu} 3.0} \right)\end{matrix}$

An included switch, like all other components, fits within the 5millimeter diameter cavity that has been machined within the shaft ofthe original hip implant. Additionally the switch will have the abilityto be turned ON and OFF once implanted within the human body. In thisexample, a magnetically based switch is selected. Coto Technologymanufactures a switch, RI-80 Series Dry Reed Switch that is designedspecifically for medical applications and which meets the design sizeconstraints. The switch has a maximum dimension of the central tube of 5millimeters in length and 1.8 millimeters in diameter. This switch willcarry a maximum current of 0.5 amperes and a has a maximum operatingvoltage of 200 volts, both of which are satisfactory operatingcharacteristics needed for a bactericidal hip implant according to theinvention.

Any patents or publications mentioned in this specification areincorporated herein by reference to the same extent as if eachindividual publication is specifically and individually indicated to beincorporated by reference. In particular, U.S. Provisional PatentApplication Ser. No. 60/585,159, filed Jul. 1, 2004, is herebyincorporated by reference in its entirety.

The compositions and methods described herein are presentlyrepresentative of preferred embodiments, exemplary, and not intended aslimitations on the scope of the invention. Changes therein and otheruses will occur to those skilled in the art. Such changes and other usescan be made without departing from the scope of the invention as setforth in the claims.

1. A medical implant system, comprising: an implant body made of abiocompatible material, the implant body having an external surface; ametal component disposed on the external surface of the implant body; aconduit for electrical current, the conduit in contact with the metalcomponent; and a power source in electrical communication with theconduit for electrical current.
 2. The medical implant system of claim1, wherein the implant body further comprises: an internal cavity, theinternal cavity having a wall and an opening; and a cap removablydisposed in the opening of the internal cavity, wherein the power sourceis disposed in the internal cavity and wherein the conduit is theimplant body.
 3. The medical implant system of claim 1, wherein theimplant body is adapted to be disposed totally within a human body whenin use.
 4. The medical implant system of claim 2, further comprising ametal component disposed on a portion of the internal cavity wall. 5.The medical implant system of claim 1, wherein the metal componentcomprises silver.
 6. The medical implant system of claim 1, wherein themetal component comprises a metal selected from the group consisting of:gold, zinc, copper, cadmium, cobalt, nickel, platinum, palladium,manganese, and chromium.
 7. The medical implant system of claim 1,wherein the metal component is a coating disposed on the externalsurface of the implant body.
 8. The medical implant system of claim 7,wherein the metal coating ranges in thickness between 1×10⁻⁹-5×10⁻⁵meters.
 9. The medical implant system of claim 7, wherein the metalcoating is disposed on a portion of the external surface of the implantbody ranging from 1-100% of the external surface of the implant body.10. The medical implant system of claim 7 wherein the metal coating isdisposed on a portion of the external surface of the implant bodyranging from 50-99% of the external surface of the implant body.
 11. Themedical implant system of claim 7, wherein the metal coating is disposedas a single region of continuous coating on the external surface. 12.The medical implant system of claim 7, wherein the implant bodycomprises an articular surface having no coating.
 13. The medicalimplant system of claim 7, wherein the metal component is in the form ofa wire disposed on the external surface.
 14. The medical implant systemof claim 1, wherein the metal component is more electrically conductivethan the biocompatible material.
 15. The medical implant system of claim1, further comprising a resistor in electrical communication with thepower source.
 16. The medical implant system of claim 1, furthercomprising a switch in electrical communication with the power source.17. The medical implant system of claim 16, further comprising acontroller in signal communication with the switch.
 18. The medicalimplant system of claim 2, wherein the cap is made of an electricallyinsulating material.
 19. The medical implant system of claim 1, furthercomprising an electrically insulating material disposed between theexternal surface of the implant body and the metal component.
 20. Themedical implant system of claim 17, wherein the controller is externalto the body of an individual having an implant body disposed therein.21. A method for inhibiting microbial infection associated with anorthopedic implant, comprising: providing a medical implant systemaccording to claim 1; delivering a current to a metal component disposedon an external surface of an implant body, the implant body located in ahuman body at a site of potential infection, wherein the delivery ofcurrent to the metal component causes release of metal ions toxic to aninfectious microbe at the site of potential infection, such thatmicrobial infection is inhibited.